Co-integration of tensile silicon and compressive silicon germanium

ABSTRACT

Integrated circuits are disclosed in which the strain properties of adjacent pFETs and nFETs are independently adjustable. The pFETs include compressive-strained SiGe on a silicon substrate, while the nFETs include tensile-strained silicon on a strain-relaxed SiGe substrate. Adjacent n-type and p-type FinFETs are separated by electrically insulating regions formed by a damascene process. During formation of the insulating regions, the SiGe substrate supporting the n-type devices is permitted to relax elastically, thereby limiting defect formation in the crystal lattice of the SiGe substrate.

BACKGROUND

Technical Field

The present disclosure generally relates to techniques for fabricatinghigh performance fin field-effect transistors (FinFETs) and, inparticular, to techniques for defect reduction in strained silicontransistors.

Description of the Related Art

Advanced integrated circuits often feature strained channel transistors,silicon-on-insulator (SOI) substrates, FinFET structures, orcombinations thereof, in order to continue scaling transistor gatelengths below 20 nm. Such technologies allow the channel length of thetransistor to be made smaller while minimizing detrimental consequencessuch as current leakage and other short channel effects.

A FinFET is an electronic switching device that features a conductionchannel in the form of a semiconducting fin that extends outward fromthe substrate surface. In such a device, the gate, which controlscurrent flow in the fin, wraps around three sides of the fin so as toinfluence current flow from three surfaces instead of one. The improvedcontrol achieved with a FinFET design results in faster switchingperformance in the “on” state and less current leakage in the “off”state than is possible in a conventional planar device. FinFETs aredescribed in further detail in U.S. Pat. No. 8,759,874, and U.S. PatentApplication Publication US2014/0175554.

Strained silicon transistors have been developed to increase mobility ofcharge carriers, i.e., electrons or holes, passing through asemiconductor lattice. Incorporating strain into the channel of asemiconductor device stretches the crystal lattice, thereby increasingcharge carrier mobility in the channel so that the device becomes a moreresponsive switch. Introducing a compressive strain into a pFETtransistor tends to increase hole mobility in the channel, resulting ina faster switching response to changes in voltage applied to thetransistor gate. Likewise, introducing a tensile strain into an nFETtends to increase electron mobility in the channel, also resulting in afaster switching response.

There are many ways to introduce tensile or compressive strain intotransistors, for both planar devices and FinFETs. In general, suchtechniques typically entail incorporating into the device epitaxiallayers of one or more materials having crystal lattice dimensions orgeometries that differ slightly from those of the silicon substrate.Strain and mobility effects within an epitaxially grown crystal aretuned by controlling the elemental composition of the crystal. Suchepitaxial layers can be incorporated into source and drain regions, intothe transistor gate that is used to modulate current flow in thechannel, or into the channel itself, which is a portion of the fin. Forexample, one way to introduce strain is to replace bulk silicon from thesource and drain regions, or from the channel, with silicon compoundssuch as silicon germanium (SiGe). Because Si—Ge bonds are longer thanSi—Si bonds, there is more open space in a SiGe lattice. The presence ofgermanium atoms having longer bonds stretches the lattice, causinginternal strain. Electrons can move more freely through a lattice thatcontains elongated Si—Ge and Ge—Ge bonds, than through a lattice thatcontains shorter Si—Si bonds. Replacing silicon atoms with SiGe atomscan be accomplished during a controlled process of epitaxial crystalgrowth, in which a new SiGe crystal layer is grown from the surface of abulk silicon crystal, while maintaining the same crystal structure ofthe underlying bulk silicon crystal. It has been determined thatepitaxial SiGe films containing a high concentration of germanium, e.g.,in the range of 25%-40%, provide enhanced electron mobility comparedwith lower concentration SiGe films. Thus, from the point of view ofdevice performance, it is generally advantageous to increase the percentconcentration of germanium atoms in the fins in a FinFET.

Alternatively, strain can be induced in the fin from below the device byusing various types of silicon-on-insulator (SOI) substrates. An SOIsubstrate features a buried insulator, typically a buried oxide layer(BOX) underneath the active area. SOI FinFET devices have been disclosedin patent applications assigned to the present assignee, for example,U.S. patent application Ser. No. 14/231,466, entitled “SOT FinFETTransistor with Strained Channel,” U.S. patent application Ser. No.14/588,116, entitled “Silicon Germanium-on-insulator FinFET,” and U.S.patent application Ser. No. 14/588,221, entitled “Defect-FreeStrain-Relaxed Buffer Layer.”

While a strained silicon lattice is beneficial, creating strain byincorporating germanium atoms using existing methods tends to damage thecrystal lattice. As a result, the lattice structures of germanium-richfilms tend to be mechanically unstable, especially if they contain ahigh number of structural defects such as faults, or dislocations.Furthermore, a mechanically unstable SiGe fin may be structurallylimited with regard to its aspect ratio, or height-to-width ratio. Sucha limitation is undesirable because one advantage of a FinFET is thatthe fin, being a vertical structure, has a small footprint.

BRIEF SUMMARY

Dislocation defects that cause mechanical instability in FinFETs can beavoided by creating a germanium-rich layer that is relaxed, as analternative to a strained film. A self-aligned SiGe FinFET device of thepresent disclosure features a strain-relaxed substrate having a highgermanium concentration. Integrated circuits are disclosed in which thestrain properties of constituent pFETs and nFETs are independentlyadjustable. The pFETs include compressive-strained SiGe on a siliconsubstrate, while the nFETs include tensile-strained silicon on astrain-relaxed SiGe substrate. Adjacent n-type and p-type FinFETs areseparated by insulating regions formed using a damascene process. Duringformation of the insulating regions, the SiGe substrate supporting then-type devices is permitted to relax elastically, thereby limitingdefect formation in the crystal lattice of the SiGe substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale.

FIG. 1 is a flow diagram showing steps in a first method of fabricatingan integrated circuit that includes compressive strained SiGe pFETstogether with tensile silicon nFETs, according to one embodiment asdescribed herein.

FIG. 2A is a top plan view of a SiGe active layer on a siliconsubstrate, according to one embodiment as described herein.

FIG. 2B is a cross-sectional view corresponding to FIG. 2A.

FIG. 3A is a top plan view of a large trench formed in the nFET regionof the silicon substrate, according to one embodiment as describedherein.

FIG. 3B is a cross-sectional view of the large trench shown in FIG. 3A.

FIG. 4A is a top plan view of an active layer of silicon indicating theorientation of fins formed below an oxide surface, according to oneembodiment as described herein.

FIG. 4B is a cross-sectional view of the active layer of silicon shownin FIG. 4A, along a cut line 4B-4B substantially parallel to a fin,according to one embodiment as described herein.

FIG. 4C is a cross-sectional view of an active layer of silicon along acut line 4C-4C across the fins, according to one embodiment as describedherein.

FIG. 5A is a top plan view of the active layer of silicon followingformation of isolation trenches between nFET and pFET regions, accordingto one embodiment as described herein.

FIGS. 5B, 5C are cross-sectional views corresponding to FIG. 5A.

FIG. 6A is a top plan view of the active layer of silicon after fillingthe isolation trenches and inter-fin regions with oxide, according toone embodiment as described herein.

FIGS. 6B, 6C are cross-sectional views corresponding to FIG. 6A.

FIG. 7A is a top plan view of the nFET and pFETs, following formation ofa polysilicon gate, according to one embodiment as described herein.

FIGS. 7B, 7C are cross-sectional views corresponding to FIG. 7A.

FIG. 8 is a flow diagram showing steps in a second method of fabricatingan integrated circuit that includes compressive strained SiGe pFETstogether with tensile silicon nFETs, according to an alternativeembodiment as described herein.

FIG. 9 is a cross-sectional view showing isolation regions between nFETand pFET devices, prior to fin formation, according to the secondfabrication method shown in FIG. 8.

FIG. 10 is a cross-sectional view showing isolation regions between nFETand pFET devices that are shallower than the intervening strain-relaxedSiGe substrate, according to one embodiment as described herein.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various aspects of thedisclosed subject matter. However, the disclosed subject matter may bepracticed without these specific details. In some instances, well-knownstructures and methods of semiconductor processing have not beendescribed in detail to avoid obscuring the descriptions of other aspectsof the present disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearance of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thespecification are not necessarily all referring to the same aspect.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more aspects of the presentdisclosure.

Reference throughout the specification to integrated circuits isgenerally intended to include integrated circuit components built onsemiconducting substrates, whether or not the components are coupledtogether into a circuit or able to be interconnected. Throughout thespecification, the term “layer” is used in its broadest sense to includea thin film, a cap, or the like and one layer may be composed ofmultiple sub-layers.

Reference throughout the specification to conventional thin filmdeposition techniques for depositing silicon nitride, silicon dioxide,metals, or similar materials include such processes as chemical vapordeposition (CVD), low-pressure chemical vapor deposition (LPCVD), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemicalvapor deposition (PECVD), plasma vapor deposition (PVD), atomic layerdeposition (ALD), molecular beam epitaxy (MBE), electroplating,electro-less plating, and the like. Specific embodiments are describedherein with reference to examples of such processes. However, thepresent disclosure and the reference to certain deposition techniquesshould not be limited to those described. For example, in somecircumstances, a description that references CVD may alternatively bedone using PVD, or a description that specifies electroplating mayalternatively be accomplished using electro-less plating. Furthermore,reference to conventional techniques of thin film formation may includegrowing a film in-situ. For example, in some embodiments, controlledgrowth of an oxide to a desired thickness can be achieved by exposing asilicon surface to oxygen gas or to moisture in a heated chamber.

Reference throughout the specification to conventional photolithographytechniques, known in the art of semiconductor fabrication for patterningvarious thin films, includes a spin-expose-develop process sequencetypically followed by an etch process. Alternatively or additionally,photoresist can also be used to pattern a hard mask (e.g., a siliconnitride hard mask), which, in turn, can be used to pattern an underlyingfilm.

Reference throughout the specification to conventional etchingtechniques known in the art of semiconductor fabrication for selectiveremoval of polysilicon, silicon nitride, silicon dioxide, metals,photoresist, polyimide, or similar materials includes such processes aswet chemical etching, reactive ion (plasma) etching (RIE), washing, wetcleaning, pre-cleaning, spray cleaning, chemical-mechanicalplanarization (CMP) and the like. Specific embodiments are describedherein with reference to examples of such processes. However, thepresent disclosure and the reference to certain deposition techniquesshould not be limited to those described. In some instances, two suchtechniques may be interchangeable. For example, stripping photoresistmay entail immersing a sample in a wet chemical bath or, alternatively,spraying wet chemicals directly onto the sample.

Specific embodiments are described herein with reference toco-integrated tensile nFETs and compressive pFETs that have beenproduced; however, the present disclosure and the reference to certainmaterials, dimensions, and the details and ordering of processing stepsare exemplary and should not be limited to those shown.

Turning now to the figures, FIG. 1 shows steps in a method 200 offabricating p-type FinFETs, or pFETs, having compressive strain,co-integrated with n-type FinFETs, or nFETs, having tensile strain,according to one embodiment. Steps 202-219 in the method 200 are furtherillustrated by FIGS. 2A-7C, and described below. In each of the Figures,A is a top plan view of co-integrated FinFETs at the present step duringfabrication, indicating cut lines for cross-sectional views; B is across-sectional view along a cut line parallel to the fins of theFinFETs; and C is a cross-sectional view along a cut line transverse tothe fins. One exemplary nFET and two exemplary pFETs are shown in eachcross-sectional view.

At 202, a blanket epitaxial SiGe film having compressive strain is grownon a silicon substrate 220 to form a compressive SiGe active layer 222.The compressive SiGe active layer 222 (cSiGe) is desirably in the rangeof about 10-100 nm thick with a target thickness of 40 nm and has a Geconcentration in the range of about 15-50%, with a target concentrationof 25% germanium. The compressive SiGe active layer 222 is a fullycompressively-strained film that will include at least one source andone drain of a p-type FinFET, and a fin channel coupling the source tothe drain.

At 204, the compressive SiGe active layer 222 and the silicon substrate220 are patterned together to open the nFET regions, and to cover thepFET regions, according to one embodiment as illustrated in FIGS. 2A,2B, 3A, and 3B. First, a blanket hard mask 224 is deposited on thecompressive SiGe active layer 222, and patterned in the usual way, usinga photoresist 226, and, optionally, an optical planarization layer(OPL). The hard mask 224, and subsequent hard masks described below, canbe made of SiN, SiO₂, or a SiO₂/SiN bi-layer. The hard mask 224 can bedeposited according to any conventional method such as, for example,plasma-enhanced CVD (PE-CVD), low pressure CVD (LP-CVD), rapid thermalCD (RT-CVD), atomic layer deposition (ALD), or the like. Then, the SiNhard mask 224 is used to etch an opening 228 into the underlyingepitaxial SiGe layer, the opening 228 extending further into the siliconsubstrate 220 to form a damascene trench having a width “a” and a depth“d.” The width can be anywhere in the range of 10 nm-100 um. The depthis desirably in the range of about 50-400 nm. The dimensions a and d maydepend on, for example, whether or not logic or SRAM devices are beingfabricated.

At 206, a thick SiGe layer 230 is formed to fill the opening 228,according to one embodiment as shown in FIGS. 4B, 4C. Filling theopening 228 completes a damascene process that forms a strained SiGelayer in the silicon substrate 220, underneath the active layer wherethe nFET will later be formed. The thick SiGe layer 230 effectivelyserves as a substrate taking the place of the silicon substrate 220. Inone embodiment, the thick SiGe layer 230 is formed by selectiveepitaxial growth from the underlying silicon substrate 220. Theselective epitaxy process proceeds from bottom to top, in the nFETregion only, stopping at the surface of the silicon substrate 220. Thehard mask 224 remains in place during the selective epitaxy process. Achlorine-based chemistry or a silane-based chemistry, for example, canbe used to suppress growth from the sidewalls of the silicon substrate220, thereby achieving a directional deposition. Such a technique fordirectional epitaxy is known to those skilled in the art of epitaxialcrystal growth. The thickness of the thick SiGe layer 230 can bemaximized without forming crystal defects by tuning the germaniumconcentration. Further optimization to maximize mechanical stress in thefin channels may entail forming a thick SiGe layer 230 that has avertical germanium concentration gradient that can be achieved byvarying an amount of germanium during the directional deposition step.Alternatively, other techniques for directional epitaxy may be used togrow the thick SiGe layer 230. The resulting inlaid thick SiGe layer 230in the nFET region has a compressive strain.

At 208, an epitaxial silicon active layer 232 is formed, according toone embodiment, as shown in FIGS. 4B and 4C. In one embodiment, theepitaxial silicon active layer 232 is also grown directionally upwardfrom the surface of the thick SiGe layer 230, while suppressing growthfrom sidewalls of the SiGe active layer 222. The epitaxial siliconactive layer 232 has a thickness target approximately equal to that ofthe surrounding compressive SiGe layer 222. The epitaxial silicon activelayer 232 is thus formed in the active region that will include a sourceand a drain of an n-type FinFET, as well as a fin channel coupling thesource to the drain. The epitaxial silicon active layer 232 can be grownas an added step in the same process as the thick SiGe layer 230, inwhich a flow of germanium gas is turned off at the transition betweenSiGe and silicon. A timed epitaxy process can be used, wherein the timefor each step is based on the desired mask opening a, and a known growthrate for each of epitaxial SiGe and epitaxial silicon. Source and drainregions of the epitaxial silicon active layer 232 may be doped in-situduring epitaxial growth. The epitaxial silicon active layer 232 thusformed is a relaxed layer, having a crystal structure similar to that ofthe substrate 220.

At 210, following the directional epitaxy steps, the hard mask 224 isremoved e.g., by any suitable method.

At 212, fins 240 are formed in the compressive SiGe active layer 222,and in the tensile silicon active layer 232, according to oneembodiment, as shown in FIGS. 4A and 4C. FIG. 4A shows a top view of thenFET and pFETs after formation of the fins 240 and an inter-fin oxide244. Although the surface is covered with a pad oxide 242, theunderlying fins 240 are indicated by dashed lines, as is the epitaxialsilicon active layer 232 which also delineates the boundaries of thethick SiGe layer 230.

In a FinFET device, the fin embodies the conduction channel, whichcouples source and drain regions to one another. To form the fins 240,shown in FIG. 4C, first the pad oxide 242 is deposited, and on top ofthe pad oxide 242, a pad nitride (SiN) layer is used as a fin hard mask(not shown) to define the fins 240 by a conventional photolithographymethod. Alternatively, the fins 240 can be defined using a sidewallimage transfer (SIT) method that is capable of producing very narrowfeatures, as is known in the art. In one embodiment, the fins 240 havefin widths in the range of about 5-20 nm. In the pFET regions, the fins240 extend vertically into the silicon substrate 220 below thecompressive SiGe active layer 222. In the nFET region, the fins 240extend vertically through the tensile silicon active layer 232 and intothe thick SiGe layer 230. Following fin formation, the pad oxide 242 andthe fin hard mask, both bearing a fin pattern, are removed. Inpreparation for the next process step, spaces between the fins 240 arefilled with the inter-fin oxide 244. The inter-fin oxide 244 is thenplanarized so as to re-establish the pad oxide 242, slightly above thefins 240 and the inter-fin oxide 244.

At 214, parallel cuts 252, substantially parallel to the fins 240, andperpendicular cuts 254, transverse to the fins 240, are made betweenpFET and nFET active regions, according to one embodiment, as shown inFIGS. 5A-5C. First, a SiN cut hard mask 250 is formed on top of the padoxide 242. The parallel cuts 252 are then patterned in the SiN cut hardmask 250, as shown in FIGS. 5A, 5C. The pattern of parallel cuts 252shown in FIG. 5A is then transferred to the substrate 220 by etching, sothat the parallel cuts 252 extend downward between the thick SiGe layer230 and the silicon substrate 220 to a cut depth 245. In FIGS. 5B, 5C,the cut depth 245 is shown slightly below the SiGe depth d. In general,however, the cut depth 245 can be less than, equal to, or greater than,the depth d of the thick SiGe layer 230, although it may be advantageousfor the cut depth 245 to be greater than the depth d of the thick SiGelayer 230.

Next, in a subsequent lithography step, perpendicular cuts 254 arepatterned in the cut hard mask 250, as shown in FIGS. 5A, 5B. Thepattern of perpendicular cuts 254, shown in FIG. 5A, is then transferredto the substrate 220 by etching, so that the perpendicular cuts 254extend downward between the thick SiGe layer 230 and the siliconsubstrate 220 to about the same cut depth 245 as the parallel cuts 252,as shown in FIG. 5B. Each one of the cuts 252, 254 thus creates threefree surfaces 253 adjacent to a lower portion of the thick SiGe layer230. The depths of the perpendicular cuts 254 can be less than, equalto, or greater than the depths of the parallel cuts 252.

As the parallel cuts 252 are made, the thick SiGe layer 230 relaxeselastically (rSiGe), either partially or fully, in a horizontaldirection parallel to the active layers 222 and 232. Such elasticrelaxation transforms the thick SiGe layer 230 from a compressivelystrained layer to a strain-relaxed SiGe region 258 inlaid in the siliconsubstrate 220. The elastic relaxation occurs without creating defects,as would otherwise occur in a conventional process that relies onplastic relaxation. Likewise, as the perpendicular cuts 254 are made,the strain-relaxed SiGe region 258 experiences a biaxial elasticrelaxation in which the SiGe fully relaxes elastically, in alldirections, again without creating defects. At the same time as the cuts252, 254 are made, the overlying epitaxial silicon active layer 232 issegmented from the compressive SiGe active layer 222, and the epitaxialsilicon active layer 232 is transformed into a biaxiallytensilely-strained film. The resulting tensile silicon active layer 243provides superior electron mobility within the nFET fins. Meanwhile, thecompressive SiGe active layer 222 on either side of the tensile siliconactive layer 243 remains fully compressively-strained to providesuperior hole mobility within the pFET fins. In this way, thecompressive strain in the pFETs and the tensile strain in the nFETs areadjusted independently.

At 216, photoresist is stripped from the cut hard mask 250 and the cuts252, 254 are filled with oxide, creating insulating regions 262, 264,respectively, according to one embodiment, as shown in FIGS. 6A-6C. Theinsulating regions 262, 264 electrically insulate the nFET and the pFETsfrom one another. The insulating regions 262, 264 have substantiallystraight, vertical sides, in contrast with the usual sloped sides. Oxidewithin the insulating regions 262, 264 is then planarized to stop on thecut hard mask 250, before the cut hard mask 250 is removed. The oxide isthen recessed further so as to remove the pad oxide 242 from the fins240. The insulating regions 262, 264 may extend beyond the tops of thefins 240, as shown in FIGS. 6B, 6C.

At 218, a gate structure 255 is formed transverse to the fins 240,according to one embodiment, as shown in FIGS. 7A-7C. The gate structure255 of the FinFET devices wraps around three sides of each fin so as tocontrol current flow therein more precisely than is possible in aconventional planar device. The gate structure 255 includes a gatedielectric 266 and a gate 268, which may be made of polysilicon, forexample. Alternatively, the gate 268 may be made of metal, or it may bemade of polysilicon initially and later replaced with metal using areplacement metal gate process as is well known in the art. First, oxidewithin the insulating regions 262, 264 is partially removed, down to thesurface of the substrate 220. Next, the gate dielectric 266, e.g., athin layer of SiO₂, HfO₂, or the like, is formed over the fins 240.Finally, a thick polysilicon gate 268 is formed on top of the gatedielectric 266, and the gate dielectric 266 and the polysilicon gate 268are patterned with features transverse to the fins, in the usual way.

At 219, the source and drain regions are doped, according to oneembodiment. The source and drain regions of the p-type compressive SiGeactive layer 222, and of the n-type tensile silicon active layer 232,can be doped by ion or plasma implantation, or combinations thereof,using the existing gate structure 255 as a mask. Alternatively, raisedsource and drain regions may be grown epitaxially from the source anddrain regions and doped in-situ. Using either technique, a self-aligneddoping step completes formation of the co-integrated nFET and pFETdevices.

FIG. 8 shows a series of steps in a method 300 of fabricating p-typeFinFETs, or pFETs, having compressive strain, co-integrated with n-typeFinFETs, or nFETs having tensile strain, according to an alternativeembodiment. In the method 300, some steps occur in a different order,for example, the fins 240 are formed after the insulating regions 262,264.

FIGS. 9 and 10 show exemplary cross-sectional views of structures 320a,b formed in accordance with the method 300 that includes steps302-320. The structures 320 a,b show the nFET and pFETs following step314, which is after completion of the insulating regions 264, but priorto formation of the fins 240 at 316. In FIG. 9, the insulating regions264 a extend to a depth 245 a below the depth, d, of the strain-relaxedSiGe region 258. In FIG. 10, the insulating regions 264 b extend to adepth 245 b above the depth, d, of the strain-relaxed SiGe region 258.The sequence of steps in the exemplary method 300 is otherwise similarto those in the method 200. As in the method 200, the insulating regions262 and 264 made by the method 300 can extend to a depth that is lessthan, equal to, or greater than, the depth of the trench that definesthe boundary of the strain-relaxed SiGe region 258, while still inducingrelaxation of the SiGe and tensile strain in the silicon active layer232.

It will be appreciated that, although specific embodiments of thepresent disclosure are described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the present disclosure. Accordingly, the present disclosure isnot limited except as by the appended claims.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

1. A method of making an integrated circuit comprising: forming acompressive SiGe active layer on a silicon substrate; forming a p-typeFinFET in the compressive SiGe active layer; forming a strain-relaxedSiGe region inlaid in the silicon substrate; forming a tensile siliconactive layer on the strain-relaxed SiGe region and adjacent to thecompressive SiGe active layer; forming an n-type FinFET in the tensilesilicon active layer; and forming electrically insulating regionspositioned between the p-type and n-type FinFETs, and between thestrain-relaxed SiGe region and the silicon substrate.
 2. The method ofclaim 1 wherein forming the tensile silicon active layer includesforming the tensile silicon active layer surrounded by the compressiveSiGe active layer.
 3. The method of claim 1 wherein forming the tensilesilicon active layer includes aligning the tensile silicon active layervertically with the strain-relaxed SiGe region.
 4. The method of claim 1wherein the insulating regions have substantially straight, verticalsides and widths in the range of 50 and 100 nm.
 5. The method of claim 1wherein forming the electrically insulating regions includes extendingthe electrically insulating regions above a top surface of the activelayers.
 6. The method of claim 1 wherein the compressive SiGe activelayer and the tensile silicon active layer have thicknesses in the rangeof 10 and 100 nm.
 7. The method of claim 1 wherein the compressive SiGeactive layer has a germanium concentration in the range of 15% and 50%.8. The method of claim 1 wherein forming the strain-relaxed SiGe regionincludes: replacing a portion of the silicon substrate in an nFET regionwith a SiGe substrate portion; and forming trenches along at least twosides of the nFET region separating at least part of the SiGe substrateportion from the silicon substrate, thereby relieving strain in the SiGesubstrate portion and inducing tensile strain in the silicon activelayer.
 9. The method of claim 8 wherein forming the electricallyinsulating regions includes forming electrically insulating material inthe trenches.
 10. The method of claim 8 wherein forming the trenchesincludes forming the trenches along four sides of the nFET region tocause biaxial elastic relaxation in the SiGe substrate portion andbiaxial tensile strain in the silicon active layer.
 11. A method,comprising: forming a blanket SiGe layer on a silicon substrate, theSiGe layer having compressive strain; masking a pFET region of the SiGelayer; replacing a portion of the silicon substrate in an nFET regionwith a SiGe substrate portion; forming an epitaxial silicon active layerover the SiGe substrate portion in the nFET region; forming trenchesalong at least two sides of the nFET region separating at least part ofthe SiGe substrate portion from the silicon substrate, thereby relievingstrain in the SiGe substrate portion and inducing tensile strain in thesilicon active layer; forming electrically insulating material in thetrenches; patterning fins in the pFET and nFET regions; and forming agate structure that wraps around three sides of the fins.
 12. The methodof claim 11 wherein patterning the fins occurs prior to forming thetrenches.
 13. The method of claim 11 wherein patterning the fins occursafter forming the trenches.
 14. The method of claim 11 wherein formingthe trenches causes elastic relaxation in the SiGe substrate portion.15. The method of claim 11 wherein trenches are formed along four sidesof the nFET region to cause biaxial elastic relaxation in the SiGesubstrate portion and biaxial tensile strain in the silicon activelayer.
 16. A method of making an integrated circuit comprising: formingfirst and second compressive SiGe active regions on a silicon substrate;forming a strain-relaxed SiGe region inlaid in the silicon substrate;forming a tensile silicon active layer on the strain-relaxed SiGe regionand between the first and second compressive SiGe active regions;forming transistors in the first and second compressive SiGe activeregions and in the tensile silicon active layer; forming a firstelectrically insulating region extending into the silicon substrate andalong a first side wall of the strain-relaxed SiGe region; and forming asecond electrically insulating region extending into the siliconsubstrate and along a second side wall of the strain-relaxed SiGeregion.
 17. The method of claim 16, wherein: forming the firstelectrically insulating region includes extending the first electricallyinsulating region between the first compressive SiGe active region andthe tensile silicon active layer, and forming the second electricallyinsulating region includes extending the second electrically insulatingregion between the second compressive SiGe active region and the tensilesilicon active layer.
 18. The method of claim 16, wherein forming thetensile silicon active layer includes aligning the tensile siliconactive layer vertically with the strain-relaxed SiGe region.
 19. Themethod of claim 16, wherein the strain-relaxed SiGe region has a firstdepth into the silicon substrate and the first and second electricallyinsulating regions having second depths that are greater than the firstdepth.
 20. The method of claim 16, wherein forming the transistorsincludes: forming a plurality of p-type FinFETs formed in the first andsecond compressive SiGe active regions; and forming a plurality ofn-type FinFETs formed in the tensile silicon active layer.